A conventional wind turbine generator that generates electricity by rotating a wind turbine with wind power and transmitting its rotary motion to a generator is provided with a yaw system that rotates (swings) a nacelle in accordance with the wind direction.
The conventional yaw system is constituted of a yaw driving unit, a yaw slew ring, and a yaw brake, whose main components are disposed at the nacelle side. That is, the nacelle fitted with a wind turbine and a powertrain that generates electricity using its rotational power is configured to rotate on the top of a tower by the operation of the yaw system and to generate electricity while pointing in an optimum direction according to the wind direction.
A conventional yaw system 10 shown in FIG. 3 is configured such that a nacelle is rotatably mounted to a tower 2, which is a fixed side, via a yaw slew ring 11 using a slide bearing 20 that also serves as a yaw brake. Reference numeral 12 in the drawing denotes a nacelle base plate that constitutes the nacelle, and the nacelle base plate 12 is tightly fitted with a yaw driving unit 15 equipped with an electric motor 13 and a drive gear 14.
The above-described slide bearing 20 is constituted of a fixed washer 21 fixed to a flange 2a of the tower 2 and a bracket 23 that holds brake pads 22. The bracket 23 in this case is a substantially L-shaped cross-section member, whose upper end surface is fixed to the lower surface of the nacelle base plate 12.
The thus-configured slide bearing 20 supports the brake pads 22 so that they can slide on the upper and lower surfaces and the outer circumferential surface of a collar 21a provided at the fixed washer 21.
In this case, a configuration example is shown in which the yaw driving unit 15 is disposed outside the tower 2, since reference sign CL in the drawing designates the axial center line of the tower 2.
Since the drive gear 14 engages with a ring gear 16 at the fixed side, the yaw driving unit 15 can rotate the nacelle (the nacelle base plate 12, the bracket 23, etc.) at the moving side, together with the drive gear 14, in accordance with the rotation of the electric motor 13 (for example, refer to Patent Document 1).
In the conventional wind turbine generator, a yaw system that adopts a rolling bearing as the above-described yaw slew ring is also known.    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2007-51585